The room temperature control unit transmits correcting variables to the bus via various communication objects, which you can use to control different controller types with switching commands or by specifying percentage values:
• Continuous 2-step control
• Switching 2-step control
• Continuous PI control
• Switching PI control
Continuous and switching 2-step control
The 2-step control is the simplest type of control. The heating switches on as soon as the actual temperature falls below a specific value, and switches off as soon as the setpoint temperature has been exceeded.
Switching 2-step control:
Continuous 2-step control:
The disadvantage of simple control, in contrast to its ad-vantage, is that the room temperature is not constant but changes continuously, reducing comfort particularly when heating and cooling systems are slow to react. To counteract this effect, you can set a sufficiently small hysteresis. However, this leads to an increase in switch-ing frequency, and therefore to increased wear of the drives.
Display heating and cooling symbol = shows current con-troller status
Display Mode
Heating active, correcting variable ≠0 Cooling active, correcting variable ≠0 (below the 1 2
symbols)
1 = Heating/cooling active, correcting variable ≠0 For two-stage heating/cooling
1 = Basic level active, correcting variable ≠0 2 = Basic level and additional level active, correcting variable ≠0
-- Insensitive zone, correcting variables = 0
Display heating and cooling symbol = shows heating/cool-ing
Display Mode Heating Cooling (below the 1 2 symbols)
1 = Heating/cooling active, correcting variable ≠0 For two-stage heating/cooling:
1 = Basic level active, correcting variable ≠0 2 = Basic level and additional level active, correcting variable ≠0
Room temperature control unit
1
0
Set point temperature Hysteresis
Correcting variable
Operating mode changed
100 %
0 % Room temperature control unit
Set point temperature Hysteresis
Correcting variable
The temperature overshoot above or below the hyster-esis apparent in the diagram is caused when the heat-ing/cooling system continues to emit heat or cold into the room after it has been switched off.
Setting rules for the 2-step control
"Hysteresis of the 2-step control" parameter:
• Small hysteresis:
Leads to small fluctuations, but frequent switching.
• Large hysteresis:
Leads to large fluctuations, but infrequent switching.
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In general, due to the influences of the heating sys-tem and the room, the sys-temperature fluctuations in the room are significantly higher than the hystere-sis.Continuous and switching PI control
For the PI control, the correcting variable is calculated from a proportional and an integral share. The calcula-tion is governed by parameters such as:
• Temperature difference between actual value and set-point
• Proportional range
• Reset time
In this way, the controller can correct the room temper-ature quickly and accurately. The corresponding cor-recting variable is transferred via a 1 bit/1 byte value to the bus.
The standard control parameters for the most common system types are already installed in the controller:
• Warm water heating
• Underfloor heating
• Electric heating
• Fan convector
• Split unit
• Cooling ceiling
You can also set the control parameters for the propor-tional range and the reset time manually, but you should know exactly which actuators are connected and the control conditions in the room.
Continuous PI control
For the continuous PI control, the corresponding 1 byte correcting variable is transmitted 0-100% directly via the bus to the heating actuator or an EMO valve drive, which convert the correcting variable directly to a de-gree of opening. However, this is only transmitted when the newly calculated correcting variable has changed by a specified percentage.
Switching PI control (PWM)
With the switching PI control, also known as the PWM control, the correcting variables calculated by the con-troller (0-100%) are converted into a pulse-width mod-ulation (PWM). Within a constant, defined cycle time, the control actuator is opened ("1") and then closed again ("0") for the calculated percentage period. For ex-ample, when a correcting variable of 25% is calculated for a cycle time of 12 minutes, a "1" is transmitted at the beginning of the cycle time, and a "0" is transmitted af-ter three minutes (= 25% of 12 minutes)
.
When the setpoint temperature changes, the controller recalculates the required correcting variable and trans-mits it still within the current cycle (broken line).
Correcting variable Calculated correcting variable
t t 100 %
50 % 0 % 100 % 50 % 0 %
1
0 Correcting variable Calculated correcting variable
t (min) t (min)
0 15 30 45 60
100 % 80%
60%
40%
20%
0 %
Setting rules for the PI control
In general:
• Large system increases (e.g. high heating output, steep characteristic curves for valves) are controlled with large proportional ranges.
• Slow heating systems (e.g. underfloor heating) are controlled with high-level reset times.
If no satisfactory control result is achieved by selecting an appropriate heating or cooling system, you can im-prove the adaptation "via control parameters":
• Small proportional range:
Large overshoot for setpoint changes (also continu-ous oscillation under certain circumstances), rapid adjustment to the setpoint.
• Large proportional range:
No (or little) overshooting, but slow adjustment.
• Short reset time:
Rapid correction of control deviations (ambient condi-tions), risk of continuous oscillation.
• Long reset time:
Slow correction of control deviations.
The framework conditions for setting the cycle time are as follows:
• For small values, the switching frequency and the bus load are increased.
• For large values, temperature fluctuations are created in the room.
• A short cycle time for rapid heating systems (e.g. elec-tric heating).
• A long cycle time for slow heating systems (e.g. un-derfloor warm water heating).
Examples
Warm water radiator heating with motorised valve drives:
Cooling ceiling with motorised valve drives:
Switching electric radiator heating:
Air conditioning with 4-duct (2-circuit) air convector sys-tem (e.g. switching valve drives):
Temperature limitation using shading facility:
t 1 t 2 Room temperature
Set point 2
Set
point 1 Time
Characteristics Parameter Setting Heating only Controller type Heating
Correcting variable
out-put Continuous PI control
Adjust the controller to
the heating system Warm water heating (5 K/150 min)
Characteristics Parameter Setting Cooling only Controller type Cooling
Correcting variable
out-put Continuous PI control
Adjust the controller to
the cooling system Adjustment via control parameter
Cooling proportional
range Approx. 5 K (depending
on the application) Reset time for cooling Approx. 240 min.
(de-pending on the applica-tion)
Characteristics Parameter Setting Heating only Controller type Heating
Correcting variable
out-put Switching PI control
Adjust the controller to
the heating system Electric heating (4 K/100 min)
Characteristics Parameter Setting Heating or
cool-ing as required, with automatic switching
Controller type Heating and cooling Correcting variable
out-put - heating e.g. switching PI control Adjust the controller to
the heating system Air convector (4 K/90 min) Correcting variable
out-put - cooling e.g. switching PI control Adjust the controller to
the cooling system Air convector (4 K/90 min) e.g.
automatical-ly switch be-tween heating and cooling
Switch between heating
and cooling automatically via the controller
Characteristics Parameter Setting Cooling only Controller type Cooling
Correcting variable
out-put - heating Switching 2-step control Hysteresis Large (e.g. 2 K)